I did check out Showhauler sort of indirectly last month. I looked at a 2001 Haulmark on a FL112 chassis which was built by Showhauler, one of the last according to the dealer. The quality was exceptional, although I didn't notice much difference between it and a 2003 built by Haulmark. I spent a few hours crawling under and around both trucks. Looking at the new Haulmark interiors, it is evident that they took a lot of ideas from their Showhauler relationship.
I do plan to take a close look at the walls. I know the exterior is a gelcoated FRP panel laminated to a substrate panel. I don't know if it is a luaun or hardboard panel. I believe they use the exterior and interior panels in a stress skin configuration, which can produce a wall of great strength in spite of using thinner panels. Of course it is also dependent on the quality of the bond to the frame, and the ability of the frame to adequately transfer and distribute loads. The Renegade uses a thicker panel, but I believe it is a three ply panel over a light gauge metal frame. The panel may be thicker, but may not perform as well as part of a stress skin wall due to the limited ability of the light-gauge frame to transfer loads to the inside panel.
I hope to get some time with the engineering department of both Haulmark and Renegade in order to better understand the design they are using. I'll pass along what I find out.
I only priced Haulmark and Renegade. The Renegade was a few thousand cheaper, but it had a 28' box. Apples to apples, they were probably pretty close.